How to append cycles render settings to another file
As far as I know there isn't a way to specifically save or append render settings. You can however append a scene from another file, that scene will bring in with it all render settings saved in it.

So you could create a file with an empty scene with all your sampling, bounce, performance settings etc. saved in it and append that scene to new files and use that scene directly.

With the appended scene as current you can also press the + button to add a new scene to your file and choose the option Copy settings, that should also create a new scene with exactly your current custom render settings copied over.

If you already have a scene setup and populated with your objects and want to apply those settings to it, your best bet is probably to create a new empty scene  from a template having your desired settings using the techniques above in the same file, then link all your objects to the new scene with the Ctrl + L Link > Objects to Scene.